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Preventing Stress Overload in Calves

Words by Karen Fraser & Stacey Cosnett - The Calf Experts


Cumulative stress has a profound impact on performance. Stress overload in young calves can have significant negative effects on their health and wellbeing. 


Calves like other animals, have limited coping mechanisms to deal with stress, and when they experience multiple stressors in a short period, it can lead to an overload that can affect health and performance, requiring a costly catch-up process. Your calves have already had several stressors in their short lives:

  1. Separation from the dam: removed from their familiar environment and source of early nutrition. 
  2. Transportation: transporting young calves, especially over long distances, can expose them to noise, vibration, temperature changes, and unfamiliar surroundings. 
  3. Handling and restraint: improper rough handling of calves during routine procedures like first-day handling, tagging, de-horning, or vaccinations can induce stress and fear responses. 
  4. Changes in diet: abrupt changes in the calf’s diet, like milk types, abrupt weaning from milk to supplements or grass. 
  5. Social stress: calves are social animals, so isolation or lack of social interaction with other calves can be stressful. Similarly, overcrowding or aggressive interactions with other calves is stressful. Large mob sizes are problematic for shyer, slower-growing calves. 
  6. Disease and health issues: calves that are sick or experiencing health problems may be more vulnerable to stress and have reduced coping abilities. They are more at risk of exposure to gut damage and have limited ability to successfully transport energy and nutrients across the gut. 


Cumulative stress from multiple sources can have a profound impact on calves compared to individual stressors. It can weaken their immune system, disrupt their digestive health, decrease weight gain, and increase susceptibility to diseases and parasites, with prolonged stress having long-term effects. 


To mitigate stress overload in young calves, it is essential to provide a well-managed and low stress environment. This includes ensuring they have proper nutrition, comfortable housing and adequate socialization, while minimising abrupt changes in routine, especially when heading into weaning.


Decreasing the milk slowly and increasing meal offered will help avoid transitioning stress. The weaning process should only start when each calf is eating 1-1.5kg (depending on size and breed) of a well-balanced calf feed for at least three consecutive days. This is the time to start decreasing milk volume, preferably over a 14-day period.


Weaning is transferring from a milk diet to a full forage/pellet diet. Factors to consider are:

  • Genetic potential 
  • The animal’s overall health 
  • Age/daily weight gain target 
  • Lean muscle development and skeletal height 
  • High volume milk programmes/overfeeders 
  • Rumen development- was it slow to develop? 
  • Supplements being offered at the right level 
  • Weather 
  • Pasture quality and quantity




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Well-grown calves are more profitable when not rushed through each stage of the weaning process. Take time weighing, paying attention to detail and treating calves as individuals when making decisions. A calf that can’t compete in a group becomes off-target, time-consuming and costly in “catch-up”.


Poor growth rates will delay the timeframe of puberty in dairy heifers and profitability in beef units. Once calves are six weeks old it is important to monitor daily gains to avoid a weakened immune defence:

  • <350g/day = underfed, effects of compounding stressors, barely maintaining. 
  • 400-600g/day = not getting enough nutrients and at risk of extra stress loading and a weakened immunity. 
  • >660g/day (depending on genetics) = growing to target, great rumen function, stronger  immune defence. 


Remember, each calf is unique, so the timing and pace of each transition may vary. Take it slow, observe their responses after each change for 14-21 days and adjust accordingly, to ensure a successful transition from milk to a well-balanced calf feed and grass.


The same slow transition back down off the hard feed is equally important - follow the same rules as weaning from being on milk. It is also a good idea to monitor parasites, coccidia and bacteria like yersinia via faecal testing during these changes and beyond.


Cumulative losses building the perfect storm:

The Perfect Storm

  • Wet weather/cloudy days: lack of vitamin D, grass nitrates rise, grass flush causing the young calf to struggle with chlorophyll. Sped-up fermentation, lack of ability to digest feed properly. 
  • Open grazing: calves in a lolly store, pick all the yummy sweet grass and overwhelmed by the sugars. 
  • Water troughs: high, unable to reach, bitter from minerals or unclean, can limit intake, growth as less dry matter consumed. 
  • Slowed rumen development: calves that over-fed on milk, thinner wall and smaller rumen size.  
  • Transitioning from milk or meal too fast: unhappy gut microbes, change in rumen function. Each transition takes a full 21 days. Grass is the most inconsistent feed for a young pre-ruminant; if the rumen was not ready then it will struggle to be able to consume enough grass and convert to energy. 


To Watch For:

  • Don’t treat calves as mobs: over-performers eating well and the under-performers getting further behind.  
  • Sudden weather changes/grass changes: can cause B1 deficiency. 
  • Don’t make decisions solely on weight; there are multiple decision-making tools for better outcomes. 
  • Offer plenty of room for all weaners to feed at same time; they move as a herd.
  • Don't wait; remove struggling calves by eye and feed better. 
  • Take faecal samples regularly - test for parasites, protozoa, bacteria. 
  • Keep water troughs clean and reachable. 
  • Break fence where possible so that the calves can learn to eat everything on offer, fewer ‘lollies’ eaten and more fibre by eating the whole sward. 


The first three months are all about setting up a functioning rumen, skeletal growth, and lean muscle development. Calves that had solely chosen to be milk/fibre eaters early-on will be on the back foot from now on, either from flush nitrogen-rich pastures low in fibre that are harder to convert, or as the pastures become reproductive, very fibrous with less protein and energy available, meaning some calves may start to struggle.


Keep under-performing calves on a good-quality pellet well beyond weaning. It is never too late to put struggling calves back onto supplements.